In the context of this patent description and the following claims, the gearshift being referred to can be, without distinction, either the rear one, which moves the chain between the different pinions associated with the rear wheel of the bicycle, or the front one, which moves the chain between the different chain rings associated with the pedal cranks.
Normally, the gearshift actuator device comprises a deformable articulated kinematic mechanism (typically an articulated quadrilateral or parallelogram) intended to be fixed to a bicycle frame and capable of taking up different operating configurations, so that the chain guide, carried by the deformable articulated kinematic mechanism, is able to take up different positions with respect to the bicycle frame (and thus with respect to the different toothed wheels) according to the different operating configurations of the deformable articulated kinematic mechanism.
The gearshift of the present invention is a motorised gearshift, in which the deformation of the deformable articulated kinematic mechanism is obtained with an electric motor that—following a suitable command input by the cyclist and through a suitable kinematic mechanism—moves different parts of the deformable articulated kinematic mechanism with respect to one another, deforming it and thus moving the chain guide.
Motorised gearshifts have been known for some time. These gearshifts, although able to have different configurations, still provide a rotary electric motor with a rotary drive shaft, the rotation of which—with suitable transmissions and reductions—is used to angularly move a rotary element of the deformable articulated kinematic mechanism or to move in translation (through screw-nut coupling) one part with respect to another of the deformable articulated kinematic mechanism, so as to determine the desired deformation of the deformable articulated kinematic mechanism.
An on-going objective of manufacturers of gearshifts is to improve the precision of actuation, upon which the ease and reliability of operation of the gearshift depends. This requirement is increasingly important the more the gearshift is intended to be used in high-level cycling competitions. In motorised gearshifts this requirement is particularly important because the deformation action of the deformable articulated kinematic mechanism is in this case very direct, without the mediation provided by the cables used in manual gearshifts.
The Applicant has realised that precision of actuation of gearshifts in which the deformation of the deformable articulated kinematic mechanism is obtained by translation of one part with respect to another can ensure greater precision. However, the Applicant has also realised that, particularly in such gearshifts, precision can be disturbed by dirt that, through use on the road, can build up on the parts of the gearshift the move with respect to one another.